Mesh deforms after automatic weights (IK and pole vector)
I think that’s the main problem is that you need to correct the Pole Angle of your IK bones or they are going to rotate crazy once in Pose mode, -90° for both right and left IK.

Also in Edit mode you need to bend the knees bones a bit forwards so that they’ll bend correctly in Pose mode. And join the 2 pole targets to your main armature. Make sure some bones (controllers, pole targets, root) won’t deform the mesh: Select each of them and disable their Deform option. And it looks like you have a lot of overlapping vertices, so altM > Merge By Distance and play with the parameters.